ISR Coverage Rotation Planner

Interactive planner for Fischer 26 ISR rotation scheduling. Calculate minimum airborne drones, coverage gaps, and stagger intervals for 24-hour persistent surveillance.

Interactive: ISR Coverage Rotation Planner

Persistent ISR Coverage with Limited Drone Fleet

The coverage rotation planner solves the scheduling problem of sustaining unbroken overhead ISR using unmanned platforms that have limited endurance. Five Fischer 26 drones with 2-hour endurance and 2.5-hour recharge time cannot all fly simultaneously — the planner calculates the optimal stagger interval so that as one drone returns for charging, another launches to replace it. The visual 24-hour timeline shows exactly when each drone is airborne (green) and charging (gray), revealing any coverage gaps where zero drones are overhead. With the default configuration (5 drones, 2h flight, 2.5h charge), the planner maintains an average of 2.2 drones airborne continuously with zero gaps — providing approximately 220 km² of persistent coverage.

Coverage Gap Analysis and Fleet Sizing

The critical metric is minimum airborne count — the worst-case number of drones flying at any point in the 24-hour cycle. If this drops to zero, there exists a time window where the brigade has no ISR coverage and is effectively blind. The planner shows that four Fischer 26 drones with the standard endurance profile produce periodic gaps of 15-20 minutes. Five drones eliminate all gaps. Six drones provide redundancy — if one drone is lost to enemy action, the remaining five maintain continuous coverage. The cost difference between four and five Fischer 26 drones is approximately 8,000 euros. The cost of a 15-minute ISR gap during which enemy armor repositions undetected is measured in lives, not euros.

Stagger Interval Optimization

The optimal stagger interval equals the total cycle time (endurance plus recharge) divided by the fleet size. For 5 drones with a 4.5-hour cycle, the stagger is 54 minutes. This means launching one drone every 54 minutes in a rolling schedule. Deviating from the optimal stagger — for example, launching two drones simultaneously after a maintenance delay — creates temporary overstaffing followed by a coverage gap. The planner's timeline visualization makes these scheduling errors immediately visible, allowing the operations officer to modify departure schedules and restore uniform coverage.

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Weather Impact on Coverage Planning

Nordic weather significantly affects Fischer 26 endurance and therefore coverage rotation planning. At -20°C, LiPo battery capacity drops to approximately 50 percent of rated value, reducing effective endurance from 2 hours to 1 hour. The coverage planner must account for this by either doubling the fleet size (10 drones instead of 5) or accepting periodic coverage gaps during extreme cold. Rain above 5mm per hour reduces optical camera effectiveness but does not affect thermal detection — the planner should recommend thermal-only ISR during precipitation. Wind above 15 m/s exceeds the Fischer 26 safe operating envelope entirely, requiring grounding of all fixed-wing ISR and switching to ground-based sensor networks.

Handoff Protocol Between Outgoing and Incoming Drones

The 54-minute stagger interval creates a 10-15 minute overlap period where both the outgoing and incoming Fischer 26 are airborne simultaneously. This overlap is intentional and critical for continuous coverage — the incoming drone must establish MANET mesh connectivity and confirm sensor functionality before the outgoing drone returns for recharge. The handoff protocol consists of four steps: incoming drone reaches operating altitude and confirms COP data feed, incoming drone verifies its YOLOv8 detection pipeline produces valid detections, outgoing drone receives handoff-complete acknowledgment, and outgoing drone begins return-to-base flight. If any step fails, the outgoing drone extends its mission until the issue is resolved, drawing on its 20 percent fuel reserve designed specifically for handoff delays.

Implementation

# ISR Coverage Rotation — Stagger Optimization
class CoverageModel:
    def __init__(self, n_drones, endurance_h, recharge_h):
        self.n = n_drones
        self.endurance = endurance_h
        self.cycle = endurance_h + recharge_h

    def airborne_at(self, t_hours):
        """Count airborne drones at time t."""
        count = 0
        for i in range(self.n):
            offset = i * (self.cycle / self.n)
            phase = (t_hours + offset) % self.cycle
            if phase < self.endurance:
                count += 1
        return count

    def min_airborne_24h(self):
        """Worst-case airborne count in 24h cycle."""
        return min(self.airborne_at(t/4) for t in range(96))

# 5× Fischer 26: 2h flight, 2.5h charge
model = CoverageModel(5, 2.0, 2.5)
stagger_min = (model.cycle / model.n) * 60
print(f"Stagger: {stagger_min:.0f} min between launches")
print(f"Min airborne: {model.min_airborne_24h()}")
print(f"Coverage: {model.min_airborne_24h() * 100} km² minimum")

Sources

• ArduPilot — ardupilot.org
• FOI — FOI publications catalogue (foi.se/publications)